The present invention relates to a core barrel for retrieving a core in a drill string.
During the drilling of the earth's formations, it is important to obtain samples of the earth at each point along the depth of the hole. Customarily, the samples are formed by using a hollow rotary drill string or drill stem having a cutting bit at the lower end thereof, which produces a core of earth within the drill string as the bit drills into the earth. The core is retrieved from within the drill string by placing an empty tube portion of a core barrel slightly above the drill bit, and after the tube is filled with the core, raising the core barrel to the earth's surface, where the contents of the tube are analyzed.
Many core barrels have been developed for retrieving cores in a drill string. Such devices ideally should be capable of being readily attached and disattached from the drill string at a particular location thereof and should be reliable in operation, not subject to breakage, and not subject to becoming snagged along the drill string. Moreover, since during the drilling operation, air or other fluid is pumped down through the drill string, around the drill bit, and up through the annulus between the drill string and the wall of the hole drilled for such purposes as removing cuttings from the bottom of the drill hole, it is also important that the core barrel permits an unimpeded flow of such air or other fluid.
The present invention was developed primarily as a result of efforts to accomplish each of the aforementioned goals associated with the design of a core barrel. A patentability search was conducted for the present invention and the following patents were uncovered:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 2,263,639 A. Muhlbach Nov. 25, 1941 3,047,081 J. N. Pitcher July 31, 1962 3,103,981 A. E. Harper Sep. 17, 1963 3,127,943 T. Mori April 7, 1964 3,485,310 V. Milosevich Dec. 23, 1969 3,701,389 Egnelov et al. Oct. 31, 1972 3,739,865 Wolda June 19, 1973 3,323,604 H. I. Henderson June 6, 1967 3,777,826 Wolda Dec. 11, 1973 3,871,487 Cooper et al. March 18, 1975 3,874,464 Sweeney April 1, 1975 3,977,482 Reed et al. Aug. 3, 1976 4,002,213 Sweeney Jan. 11, 1977 4,187,919 Lambot Feb. 12, 1980 4,276,932 Saliger et al. July 7, 1981 4,281,722 Turker et al. Aug. 4, 1981 ______________________________________
U.S. Pat. Nos. 3,739,865 and 3,777,826, both of which are to Wolda, disclose a wire line core barrel. The core barrel includes a pair of resilient latch fingers which are normally retracted away from the drill string. The core barrel is adapted to seal off the drill string and is provided with an actuator adapted to move from a first position to a second position when pressure of the fluid in the drill string above the core barrel exceeds a certain, selected pressure. When the actuator is in the second position, it forces the latch finger outwardly and into a pair of latch seats in the drill string. The section of the core barrel including the latch fingers is connected through bearing means to a core sample container so that when the section including the latch fingers rotates with the drill string, the core sample container will remain relatively stationary. When the core sample container is completely filled with a core, an upward pressure force is applied to the core sample container. This upward force is transmitted to the actuator which is moved back into its first position whereupon the latch fingers tend to snap back naturally away from the drill string and the latch seats therein. A spring may be included in the core barrel assembly to counteract any upward force applied to the core sample container and to resist movement of the actuator until a sufficiently strong force is applied thereto. A pair of holes 80, 82 and 44, 46 in the '865 and '826 patents respectively are provided in the core barrel to permit fluid flow from above and outside the core barrel to the drill bit below the core barrel.
Wolda's U.S. Pat. No. 3,777,826 further discloses a spring which acts upon the actuator such that it tends to bias the same in a position whereby the core barrel seals the drill string.
U.S. Pat. No. 3,485,310 to Milosevich, U.S. Pat. No. 3,127,943 to Mori, U.S. Pat. No. 3,871,487 to Cooper et al., U.S. Pat. No. 2,263,639 to Muhlbach, U.S. Pat. No. 3,701,389 to Egnelov et al., U.S. Pat. No. 3,977,482 to Reed et al., and U.S. Pat. No. 4,187,919 to Lambot each disclose a wire line core barrel having spring biased latching mechanisms for attaching the core barrel to a drill string.
U.S. Pat. No. 3,047,081 to Pitcher discloses a head for a core sampler tube which has a fluted periphery.
U.S. Pat. No. 3,103,981 to Harper discloses a wire line core barrel assembly having spring biased latching dogs, which dogs are mounted on and rotatable about a pin that is slightly smaller than the hole in the dog through which the pin extends. When the dogs are in a latching position, upward forces applied to the wire line core barrel are transmitted through the dogs, and not the pin.
The remaining patents disclose oil well apparatus of a more general interest.
Filed concurrently with this application and constituting part of the file wrapper of this application are a few snap-shot photographs of three wire line core barrel assemblies: a working embodiment of the present invention, and two competitor's models currently and commonly used in the field. One of the competitior's models includes a pair of spring biased latch dogs and an annular, protruding landing shoulder separating an ingress hole and an egress hole in the assembly. The landing shoulder is designed to rest upon and abut a corresponding landing ring on the interior wall of the drill string. Fluid within the drill string must flow throughout the ingress hole and back out the egress hole, thereby providing a relatively inefficient means for the flow of air or other fluid past the wire line latch assembly. The above-described '482 patent to Reed et al. discloses a core barrel having such ingress and egress holes (see Column 4, lines 54-58 thereof). The other competitor's model includes a cylindrical block to the periphery of which are attached four longitudinally extending locking prongs. The locking prongs are slightly radially outwardly biased to contact the interior wall of the drill string and to hang the wire line core barrel assembly by attachment to the drill string at a preselected location therein without any use of a landing ring. Several problems are associated with this device. Because the prongs are long and the latch assembly freely rotates within the drill string, the prongs are twisted, which sometimes causes the prongs to break or causes the bolts holding the prongs to the cylindrical block to loosen and thus stimulate prong disattachment or breakage. Also, the cylindrical block is formed with a flat upper longitudinal end, thereby providing a source of great friction and turbulence for any air or other fluid passing through the drill string.
The Patent Examiner is encouraged to review each of the above-listed patents and the snap-shot photographs accompanying this application for his own independent evaluation concerning the relevance thereof to the present invention.